1. Field of the Invention
The present invention relates to an integrated circuit which induces hysterisis in order to generate a reference voltage. More specifically, an input signal is used to provide a first voltage to a circuit, such as a driver or receiver circuit. The first voltage is also manipulated to create a second voltage which is used by the circuit as a reference.
2. Description of Related Art
Many circuits exist which require more than a single input in order to operate correctly. For example, differential amplifiers are well known and commonly used as driver or receiver circuits in computer systems employing integrated circuit (IC) technology.
Differential amplifiers are basic circuits which by their very nature require that a "difference" in signals be present which varies over time. This difference is then used to provide a reference by which an output signal can be provided which is proportional to the difference.
Typically, a first voltage input is received by the differential amplifier circuit which is considered to be an input digital signal, i.e. a specific voltage or the absence of a voltage (the presence of a voltage indicates logical "1" and the absence of voltage indicates logical "0"). An absence of a voltage may mean a particular reference voltage and is not intended to mean a floating voltage which may occur when there is no connection, or no input coming in. A second voltage input is also required as a reference. Conventional circuits use a separate voltage source which is provided by an independent and distinct power supply.
An ordinary complementary metal oxide semiconductor (CMOS) differential circuit has a very small hysterisis bandwidth, about 200 millivolts around the point where the voltage equals Vdd/2. There are two main reasons. First, the reference voltage stays constant (usually at Vdd/2) and second, only a few hundred millivolts on either side of the reference voltage of the input will switch the circuit. Furthermore, conventional differential circuits need a separate circuit line, or rail, at a different potential to be used as a reference. At very high speed operations, e.g. greater than 100 MHz noise (e.g. crosstalk, reflections, and the like) increases. For some off-chip networks, particularly multi-drop nets, the relatively small hysterisis band width of 200 mV is not large enough. When the differential circuit is used as a receiver in unterminated far-end transmission line, fault switching may occur at receivers on the near-end of the transmission line. Further, because of high wiring density of multichip modules (MCM) it is difficult for another line, or rail having a different potential to be fabricated in the MCM, due to the need to minimize the footprint of the module.
FIG. 1 is a typical prior art differential amplifier as shown generally by reference numeral 1. It can be seen that a first voltage v.sub.1 is provided by power supply 3 and a second voltage v.sub.2 is provided by a second power supply 5. A voltage differential is then output across v.sub.01 and v.sub.02. The actual operation of a differential amplifier is well known in the art and will not be described further. See "Electronic Circuits; Discrete and Integrated", second edition, D. L. Schilling and C. Belove, McGraw-Hill, 1979, pps. 304-324. Those skilled in the art will readily comprehend why it would be advantageous to have a circuit that could provide an input voltage and a reference voltage from a single source, without the necessity of separate and distinct power supplies, as disclosed by the prior art systems.